Iran’s atomic energy chief Ali Akbar Salehi, who helped forge the 2015 nuclear agreement, warned the United States on June 23 against upsetting the balance of power in the Middle East by siding with arch-rival Saudi Arabia.

Writing in the Guardian newspaper, Salehi said Tehran views a “lavish" deal U.S. President Donald Trump's administration recently announced to sell Saudi Arabia $110 billion in weapons as "provocative."

"This is especially the case if the national defense efforts of Iran...are simultaneously opposed and undermined," he said, alluding to steps the Trump administration has taken to increase U.S. sanctions on Iran for developing ballistic missiles even as it has ramped up arms sales to Riyadh and its allies.

"It would be unrealistic to expect Iran to remain indifferent to the destabilizing impact of such conduct," said Salehi, an MIT graduate who has also served as Iran's foreign minister and was a senior negotiator on the nuclear deal.

Salehi stressed that Washington's strong tilt toward Tehran's rivals in the Middle East not only risks setting off a regional arms race and "further tension and conflict" in the region, but it imperils the "hard-won" nuclear deal, which took two years to negotiate.

If the nuclear deal is to survive, he said the West must change course. "The moment of truth has arrived."

Trump, who visited Saudi Arabia on his first trip as president earlier this month, seems largely unconcerned that his showy support for the kingdom threatens to blow up the nuclear accord or set off a renewed arms race in the Middle East. He has openly shown distrust both for Iran's leaders and the nuclear deal.

Trump and the Saudis frequently blame Iran for wars ranging from Yemen to Syria, as well as for restive minority Shi'ite populations within the borders of the kingdom and other Persian Gulf states ruled by Sunni Muslims.

The Saudis, like Trump, were strongly opposed to the nuclear deal. But while Trump has promised to “dismantle the disastrous deal,” he has not so far taken any concrete steps to do so.

His administration has indicated it will adhere to the deal, which requires Iran to curb its nuclear activities in exchange for the lifting of international sanctions, as long as Tehran continues to do so.

But Salehi's article in the Guardian suggested that Iran's so far strict honoring of the deal may come into doubt in the future if the United States continues to disregard Iran’s "genuine security concerns" and "stokes Iranophobia" in the region.

Salehi urged the United States and its Western partners to "save" the nuclear deal with "reciprocal gestures" showing a commitment to engagement with Iran.

Iranian voters recently showed their preference for improved relations with the West by re-electing President Hassan Rohani with his pro-engagement platform, but “engagement is simply not a one-way street and we cannot go it alone," Salehi said.

At the same time, Iran's Supreme Leader, Ali Khamenei and his hardline supporters have ratcheted up their anti-U.S. rhetoric and use of threatening language against Saudi Arabia and Israel.

It is Khamenei who controls the armed forces, most intelligence agencies and has unquestionable track record in dictating foreign policy.

"Unfortunately, as things stand at the moment in the region, reaching a new state of equilibrium might simply be beyond reach for the foreseeable future,” Salehi said.